Secondary battery and capacitor utilizing indole compounds

ABSTRACT

The present invention provides a secondary battery and a capacitor which may provide an excellent high rate and cycle characteristic as well as sufficient electromotive force and capacity. The secondary battery and a capacitor have an active material of an electrode comprising a trimer compound comprising three units of indole or indole derivatives in condensed ring form, wherein the second position and the third position of each unit form a six-membered ring, and a proton which can be utilized as a charge carrier of the trimer compound.

TECHNICAL FIELD

[0001] The present invention relates to a secondary battery and acapacitor, more particularly utilizing an indole compound as an activematerial of an electrode and a proton as a charge carrier.

BACKGROUND OF THE INVENTION

[0002] Indole polymers are known as excellent materials for an activematerial of electrode in the light of electromotive force and capacity.However, the battery wherein the indole polymers are utilized as anactive material has not been satisfactory in the light of a rapid chargeand discharge and a cycle characteristic.

SUMMARY OF THE INVENTION

[0003] According to the present invention, a battery and a capacitorwhich may provide an excellent high rate and cycle characteristic aswell as sufficient electromotive force and capacity can be provided.

[0004] According to one aspect of the present invention, the inventionprovides a secondary battery and a capacitor having an active materialof an electrode comprising a trimer compound comprising three units ofindole or indole derivatives in condensed ring form, wherein the secondposition and the third position of each unit form a six-membered ring,and a proton which can be utilized as a charge carrier of the trimercompound.

[0005] According to another aspect of the present invention, theinvention provides a secondary battery and a capacitor comprising:

[0006] a first electrode with a first electrode active material;

[0007] a second electrode with a second electrode active material; and

[0008] an electrolyte intermediate between the first electrode and thesecond electrode, the electrolyte including a proton source material;

[0009] wherein the first electrode active material and the secondelectrode active material undergo a reversible oxidation-reductionreaction, and

[0010] both or one of the first and second electrode active materialscomprise a trimer compound comprising three units of indole or indolederivatives in condensed ring form, wherein the second position and thethird position of each unit form a six-membered ring.

[0011] According to another aspect of the present invention, theinvention provides a secondary battery and a capacitor, wherein thereceipt and release of electrons in accordance with theoxidation-reduction reaction of the trimer compound are carried out onlyby the bonding and elimination of the proton bonded to the trimercompound.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a schematic cross section showing a working example of abattery and a capacitor of this invention.

[0013]FIG. 2 is the cyclic voltamogram of the positive electrodes in theexample 1 and the comparative example 1.

[0014]FIG. 3 is the graph showing the results of charge and dischargetests (discharge curves) of the battery in the example 1.

[0015]FIG. 4 is the graph showing the results of charge and dischargetests (discharge curves) of the battery in the example 3.

[0016]FIG. 5 is the graph showing the results of charge and dischargetests (discharge curves) of the battery in the comparative example 1.

[0017]FIG. 6 is the graph showing the results of charge and dischargetests (discharge curves) of the battery in the comparative example 3.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0018] Preferred embodiments of the invention are explained in thefollowing:

[0019]FIG. 1 is a cross section of a secondary battery or a capacitoraccording to this invention. A positive electrode material layer 2 and anegative electrode material layer 4, which are formed on a currentcollector 1 and a current collector 6 respectively, are arranged so asto face each other via a separator 3; there are provided a gasket 5 madeof insulating rubber on the side of the layers wherein the positiveelectrode material layer 2 and the negative electrode material layer 4are piled via the separator 3. The positive electrode material layer 2(positive electrode) and the negative electrode material layer 4(negative electrode) are each impregnated with an electrolyte solutioncontaining protons.

[0020] A trimer compound, wherein bonds are formed among the secondposition and the third position of each unit of indole or indolederivatives, hereinafter described as an “indole trimer” can berepresented by the following general formula (1):

[0021] wherein each R represents a hydrogen atom or a substituent,independently.

[0022] The indole trimers can be prepared by known electrochemical orchemical methods utilizing known reactions such as electrochemicaloxidation, chemical oxidation, condensation reaction and substitutionreaction depending on the substituents from, for example, indole orindole derivatives, hereinafter described as an “indole monomer”represented by general formula (2) shown below. The indole trimers areprepared usually from indole monomers wherein each R attached to thesecond position and the third position is a hydrogen atom.

[0023] wherein each R represents one of a hydrogen atom, halogen atom,hydroxyl, carboxyl, sulfonic acid group, sulfuric acid group, nitro,cyano, alkyl, aryl, alkoxyl, amino, alkylthio and arylthio,independently.

[0024] The indole trimers in this invention can be represented by, forexample, general formula (1) wherein each R represents a hydrogen atom,halogen atom, hydroxy, carboxyl, sulfonic acid group, sulfuric acidgroup, nitro, cyano, alkyl, aryl, alkoxyl,amino, alkylthio and arylthio,independently. The substituents R in general formula (1) may originatefrom indole monomers utilized as raw materials.

[0025] The halogen atoms of R in general formulas (1) and (2) are, forexample, fluorine, chlorine, bromine, and iodine. Alkyl groups of R inthe formulas are, for example, methyl, ethyl, propyl, isopropyl,n-butyl, s-butyl, isobutyl, t-butyl, n-pentyl, n-hexyl, n-heptyl andn-octyl. Alkoxyl groups of R in the formulas are groups represented by—OX wherein X are, for example, the alkyl groups described above. Arylgroups of R in the formulas are, for example, phenyl, naphthyl, anthryland phenanthryl. Alkyl groups in the alkylthio groups of R in theformulas are, for example, the alkyl groups described above. Aryl groupsin the arylthio groups of R in the formulas are, for example, the arylgroups described above.

[0026] A conductive auxiliary material is added to the electrodes toprovide them with electrical conductivity, if necessary. The conductiveauxiliary material is, for example, an electrical conductive materialsuch as, crystal carbon, carbon black and graphite. Furthermore, bindermay be added to keep moldability of the electrodes and to fix thesematerials on a current collector.

[0027] Mixing ratio of constituting materials in the electrodes may bearbitrary as long as the required characteristic is obtained. However,in the light of an efficiency per unit weight or volume a preferablecomposition ranges 30 to 95 wt % of an indole trimer, 5 to 50 wt % of aconductive auxiliary material and 0 to 20 wt % of a binder.

[0028] An aqueous or nonaqueous solution containing protons ispreferably used as an electrolyte solution, so that the protons may beused as charge carriers of indole trimers. Furthermore, a concentrationof protons in the electrolyte solution is preferably 10⁻³ mol/l to 18mol/l. Salt or surface active agents may be added to the electrolytesolution to increase the electric conductivity or other properties.

[0029] Any material having an electrical insulating property and havingor providing ionic conductivity, for example, a porous film made ofpolyethylene or polytetrafluoroethylene is used as a separator saturatedwith an electrolyte solution. An electrolyte such as a gel electrolyteor solid electrolyte as sandwiched between the electrodes may besubstituted for the separator.

[0030] The indole trimer in this invention is doped by anelectrochemical or a chemical method as illustrated by the reactionformula described below. X⁻ in the formula represents a dopant ion, forexample, a sulfuric ion, a halide ion, a perchloric ion andtrifluoroacetic ion and is not limited to these ions as long as itprovides the indole trimer with an electrochemical activity by doping.

[0031] The indole trimer doped by this method generates anelectrochemical reaction accompanied with an adsorption and desorptionof a proton as illustrated by the following reaction formula 2. Only theadsorption and desorption of a proton in the indole trimer concern withthe receipt and release of electrons accompanied with anoxidation-reduction reaction of the indole trimer. Since a transfermaterial in the electrochemical reaction is only a proton in the batteryand the capacitor of this invention using the indole trimer as anelectrode material wherein the electrochemical reaction occurs, a volumechange of electrodes accompanying the reaction is less and has anexcellent cycle characteristic. Furthermore, a high mobility of a protonand a rapid chemical reaction result in an excellent high ratecharacteristic, i.e., a characteristic of a rapid charge and dischargeof the battery.

[0032] The followings are examples of the battery in this inventionwhich are explained in more detail, and it may also be possible toconstruct a structure suitable for a capacitor by setting the capacityand the rate of charge-discharge properly.

EXAMPLE 1

[0033]FIG. 1 shows a battery having the structure described above whichwas manufactured according to a usual method. Gaskets 5 made ofinsulating rubber were used as exterior material and current collectors1 and 6 were made of conductive rubber. A separator constituted ofporous film impregnated with an electrolyte solution of 40% sulfuricacid was used.

[0034] An indole trimer consisting of a 6-nitroindole trimer was used asan active material in the positive electrode material layer 2 and carbonfibers grown in gas phase were used as a conductive auxiliary materialtherein.

[0035] Quinoxaline polymer represented by the formula described belowwas used as an active material in the negative electrode material layer4 and carbon black was used as a conductive auxiliary material therein.When an indole trimer is used in the positive electrode, an activematerial used in the negative electrode is not limited to the materialif it is active electrochemically and undergoes a reversibleoxidation-reduction reaction. A mixing ratio of an active material to aconductive auxiliary material constituting electrodes was chosen asweight ratio of 75:25 (an active material: a conductive auxiliarymaterial) both in the positive and the negative electrodes.

[0036]FIG. 2 shows a cyclic voltamogram (hereinafter described as “CV”)of the positive electrode material layer 2 in an acid aqueous solution.In the reaction range 1(200-800 mV vs. Ag/AgCl) doping and dedoping ofdopant ions occur as represented by the reaction formula 1 and anelectric current associated with them is observed. In the reaction range2 (800-1200 mV vs. Ag/AgCl) adsorption and desorption of protons occuras represented by the reaction formula 2.

[0037] Charge and discharge tests were conducted to evaluate the batterymanufactured. A charging was conducted up to 1.2 V at a constantelectric current of 10 mA/cm² and discharging was conducted at constantelectric currents of 1 mA/cm² to 200 mA/cm². The results of the testsare shown in FIG. 3. The discharge capacities are based on the weight ofactive material. The tests results of discharge capacities down to 0.9Vare shown in Table 1.

[0038] An increase in a discharge current from 1 mA/cm² to 200 mA/cm²resulted in a decrease in the discharge capacity from 78 mAh/g to 62mAh/g with a decreasing rate of only 20%. The battery of this inventionusing an indole trimer in the positive electrode exhibited an excellenthigh rate characteristic.

[0039] Cycle tests were conducted repeating charging up to 1.2 V anddischarging down to 0.9 V at a constant charge-discharge current of 10mA/cm². As a result of the tests the number of cycles was 31000 untilthe final capacity reached 80% of the initial capacity. The battery ofthis invention using an indole trimer in the positive electrode had anexcellent cycle characteristics.

[0040] An indole trimer, which has a constant molecular weight andmolecular size, is different from an active material of a polymer havinga molecular weight distribution and can exist in a crystallizedstructure or in a similar arrangement in an electrode. The transfer pathof a reacting ion, i.e., a proton in the electrode is, therefore, nearlylinear and its decrease in the mobility is less. On the other hand, thepolymer material in the electrode is in an amorphous state and thetransfer path of a reacting ion has to be bypassed by polymer chainsarranged at random. Furthermore, in the case of using the indole trimeras an electrode material the conductivity of the electrode is higher andthe transfer of electrons is easier than in the case of using indolepolymers as shown in Table 1. The transfer velocity of ions andelectrons becomes higher by using the indole trimer as an electrodematerial resulting in an increase in a reaction rate which makes itpossible to manufacture a battery having an excellent high ratecharacteristic.

[0041] An indole trimer is constructed by a five-membered ring unit anda six-membered ring unit having a resonance structure over the entiremain skeleton. Therefore, the indole trimer has a higher chemicalstability and is hardly deteriorated compared with an electrode materialwhich has no resonance structure in the main skeleton. Furthermore,since the indole trimer has a higher solubility in organic solvents dueto the lower molecular weight compared with a polymer material and itschemical property such as solubility is unity because of its constantmolecular weight, it is possible to reduce contaminants easily such asmetal elements coming from oxidizing agents during preparation inaddition to easy purification. It is, therefore, possible to manufacturea battery having an excellent cycle property.

EXAMPLE 2

[0042] A similar battery was manufactured as in Example 1 except forusing an indole trimer consisting of a 5-cyanoindole trimer as an activematerial in the positive electrode material layer 2.

[0043] Charge and discharge tests were conducted according to the samemethod as in Example 1. A list of discharge capacities down to 0.9V isshown in Table 1. An increase in a discharge current from 1 mA/cm² to200 mA/cm² results in a decrease in the discharge capacity from 86 mAh/gto 72 mAh/g with a decreasing rate of only 16%.

[0044] Cycle tests were conducted repeating charging up to 1.2 V anddischarging down to 0.9 V at a constant charge-discharge current of 10mA/cm². As a result of the tests the number of cycles was 25000 untilthe final capacity reached 80% of the initial capacity.

[0045] In a battery using an indole polymer made of the same indolemonomer (Comparative Example 2), an increase in a discharge current from1 mA/cm² to 200 mA/cm² results in 25% decrease in the capacity. On theother hand, the decrease in the capacity of this example indicates only16% and the cycle characteristic in this example is 25000 cyclesresulting in the improvement of 10000 cycles compared with that inComparative Example 2.

EXAMPLE 3

[0046] A similar battery was manufactured as in Example 1 except forusing a propylenecarbonate solution wherein 1 mol/l oftetraethylammonium tetrafluoroborate and 0.1 mol/l of trifluoroaceticacid were dissolved (hereinafter described as “PC solution”).

[0047] Charge and discharge tests were conducted to evaluate the batterymanufactured. The battery was charged up to 2.3 V at a constant currentof 10 mA/cm² and discharged at constant currents of 1 to 200 mA/cm². Theresults of the tests are shown in FIG. 4 and the data of the capacitiesdown to 0.5 V are listed in Table 1.

[0048] An increase in a discharge current from 1 mA/cm² to 200 mA/cm²results in a decrease in a discharge capacity from 70 mAh/g to 39 mAh/gindicating 44% decrease in the capacity.

[0049] Cycle tests were conducted repeating charging up to 2.3 V anddischarging down to 0.5 V at a constant charge-discharge current of 10mA/cm². As a result of the tests the number of cycles was 19000 untilthe final capacity reached 80% of the initial capacity.

[0050] In a battery using a PC solution as an electrolyte solution andan indole polymer made of the same indole monomer (Comparative Example3) an increase in a discharge current from 1 mA/cm² to 200 mA/cm²resultsin 73% decrease in the capacity. On the other hand, the decrease in thecapacity of this example indicates 44% and the cycle characteristics inthis example is 19000 cycles resulting in the improvement of 7000 cyclescompared with that in Comparative Example 3.

COMPARATIVE EXAMPLE 1

[0051] A similar battery was manufactured as in Example 1 except forusing an indole polymer, i.e., poly-6-nitroindole as an active materialin the positive electrode material layer 2.

[0052] Charge and discharge tests were conducted according to the samemethod as in Example 1. The tests results of discharge capacities downto 0.9V are shown in Table 1. An increase in a discharge current from 1mA/cm² to 200 mA/cm² results in a decrease in a discharge capacity from77 mAh/g to 44 mAh/g with a decreasing rate of 43%.

[0053] Cycle tests were conducted in the same method as in Example 1 andthe test results indicated that the number of cycles was 24000 until thefinal capacity reached 80% of the initial capacity.

COMPARATIVE EXAMPLE 2

[0054] A similar battery was manufactured as in Example 1 except forusing an indole polymer, i.e., poly-5-cyanoindole as an active materialin the positive electrode material layer 2.

[0055] Charge and discharge tests were conducted according to the samemethod as in Example 1. The test results of discharge capacities down to0.9V are shown in Table 1. An increase in a discharge current from 1mA/cm² to 200 mA/cm² results in a decrease in the discharge capacityfrom 85 mAh/g to 64 mAh/g with a decreasing rate of 25%.

[0056] Cycle tests were conducted in the same method as in Example 1 andthe test results indicated that the number of cycles was 15000 until thefinal capacity reached 80% of the initial capacity.

COMPARATIVE EXAMPLE 3

[0057] A similar battery was manufactured as in Example 1 except forusing an indole polymer,i.e., poly-6-nitroindole as an active materialin the positive electrode material layer 2 and a PC solution as anelectrolyte wherein 1 mol/l of tetraethylammonium tetrafluoroborate and0.1 mol/l of trifluoroacetic acid were dissolved.

[0058] Charge and discharge tests were conducted according to the samemethod as in Example 1. The test results of discharge capacities down to0.9V are shown in Table 1. An increase in a discharge current from 1mA/cm² to 200 mA/cm² results in a decrease in the discharge capacityfrom 67 mAh/g to 18 mAh/g with a decreasing rate of 73%.

[0059] Cycle tests were conducted in the same method as in Example 1 andthe test results indicated that the number of cycles was 12000 until thefinal capacity reached 80% of the initial capacity. TABLE 1 Capacity(mAh/g) charge/ charge/ charge/ charge/ Electrode discharge dischargedischarge discharge conduc- current current current current Cycle tivityElectrolyte Voltage density density density density property (S/cm)solution (V) 1 mA/cm² 10 mA/cm² 100 mA/cm² 200 mA/cm² (cycle) Example 14.2 aq. solution 1.2 78 76 68 62 31000 2 5.2 aq. solution 1.3 86 84 7972 25000 3 4.2 PC. solution 2.2 70 68 60 39 19000 Comparative 2.7 aq.solution 1.2 77 74 63 44 24000 Example 1 2 3.5 aq. solution 1.3 85 84 7764 15000 3 2.7 PC. solution 2.2 67 63 52 18 12000

1-5. (canceled).
 6. A capacitor having an active material of anelectrode comprising a trimer compound comprising three units of indoleor indole derivatives in condensed ring form, wherein the secondposition and the third position of each unit form a six-membered ring,and a proton which can be utilized as a charge carrier of the trimercompound.
 7. The capacitor as claimed in claim 6, wherein the receiptand release of electrons in accordance with the oxidation-reductionreaction of the trimer compound are carried out only by the bonding andelimination of the proton bonded to the trimer compound.
 8. Thecapacitor as claimed in claim 6, wherein the trimer compound isrepresented by the following general formula(1):

wherein each R represents a hydrogen atom or a substituent,independently.
 9. The capacitor as claimed in claim 6 comprising anelectrode containing 30 wt % to 95 wt % of the trimer compound.
 10. Thecapacitor as claimed in claim 6 comprising a solution containing 10-3mol/l to 18 mol/l of proton as the electrolyte.
 11. (canceled)
 12. Acapacitor comprising; a first electrode with a first electrode activematerial; a second electrode with a second electrode active material;and an electrolyte intermediate between the first electrode and thesecond electrode, the electrolyte including a proton source material;wherein the first electrode active material and the second electrodeactive material undergo a reversible oxidation-reduction reaction, andboth or one of the first and second electrode active materials comprisea trimer compound comprising three units of indole or indole derivativesin condensed ring form, wherein the second position and the thirdposition of each unit form a six-membered ring.
 13. (canceled). 14.(canceled).
 15. An electrochemical cell having an active material of anelectrode comprising a trimer compound comprising three units of indoleor indole derivatives in condensed ring form, wherein the secondposition and the third position of each unit form a six-membered ring,and a proton which can be utilized as a charge carrier of the trimercompound.
 16. An electrochemical cell comprising: a first electrode witha first electrode active material; a second electrode with a secondelectrode active material; and an electrolyte intermediate between thefirst electrode and the second electrode, the electrolyte including aproton source material; wherein the first electrode active material andthe second electrode active material undergo a reversibleoxidation-reduction reaction, and both or one of the first and secondelectrode active materials comprise a trimer compound comprising threeunits of indole or indole derivatives in condensed ring form, whereinthe second position and the third position of each unit form asix-membered ring.